Selumetinib in Patients Receiving Pemetrexed and Platinum-based Chemotherapy in Advanced or Metastatic KRAS Wildtype or Unknown Non-Squamous NSCLC

Inclusion Criteria: * Patients must have histologically and/or cytologically confirmed non-squamous, KRAS wildtype or unknown, non-small cell lung cancer that is stage IIIB or IV, metastatic or unresectable and for which standard curative measures do not exist. * All patients must have a formalin fixed paraffin embedded tumour block (from primary or metastatic tumour) available for correlative studies and must have provided informed consent for the release of the block for correlative studies. * Patients must have at least one site of disease which is unidimensionally measurable as follows: * Measurable disease defined as at least one target lesion that has not been irradiated or has progressed after radiation and can be accurately measured in at least one dimension by RECIST 1.1 criteria. * Chest X-ray ≥ 20 mm * CT/MRI scan (with slice thickness of \< 5 mm) ≥ 10 mm --\> longest diameter * Physical exam (using calipers) ≥ 10 mm * Lymph nodes by CT scan ≥ 15 mm --\> measured in short axis * Presence of clinically and/or radiologically documented disease (marker positive only patients are not eligible). All radiology studies must be performed within 28 days prior to randomization (within 35 days if negative). * Age ≥ 18 years. * ECOG performance status 0 or 1 * Previous Therapy Surgery: Previous major surgery is permitted provided it has been at least 14 days prior to patient randomization and that wound healing has occurred. Radiation: Prior external beam radiation is permitted provided a minimum of 4 weeks has elapsed between the last dose and enrollment to the trial. Chemotherapy and systemic therapy: Prior therapy with ALK inhibitors is permissible. Patients may not have received prior MEK inhibitors or any other tyrosine kinase inhibitor (including EGFR inhibitors of any kind). Patients may have received vaccines, immunotherapy or other agents that are not MEK/tyrosine kinase inhibitors in the adjuvant setting or for advanced or metastatic disease. Prior adjuvant platinum-based chemotherapy or combined chemoradiotherapy with curative intent is permissible provided completed at least one year prior to enrollment. No prior cytotoxic chemotherapy for advanced / metastatic disease is permissible. \- Laboratory Requirements (must be done within 7 days prior to randomization) Neutrophils ≥ 1.5 x 10\^9/L Platelets ≥ 100 x 10\^9/L Biochemistry: Creatinine Clearance\* ≥ 50 ml/min Total bilirubin ≤ 1.5 x ULN AST and ALT ≤ 2.5 x ULN (if liver metastases ≤ 5x UNL permissible providing ALP also ≤ 6 x UNL) \* Creatinine clearance to be measured directly by 24 hour urine sampling or as calculated by appropriate formula below: Females: GFR = 1.04 x (140-age) x weight in kg/serum creatinine in μmol/L Males: GFR = 1.23 x (140-age) x weight in kg/serum creatinine in μmol/L * Patient consent must be appropriately obtained in accordance with applicable local and regulatory requirements. Each patient must sign a consent form prior to enrollment in the trial to document their willingness to participate * Patients must be accessible for treatment and follow-up. Patients randomized on this trial must be treated and followed at the participating centre * In accordance with CCTG policy, protocol treatment is to begin within 2 working days of patient randomization Exclusion Criteria: * Patients with a history of other untreated malignancies or malignancies which required therapy within the past 2 years * No symptomatic brain metastases or spinal cord compression. Patients with asymptomatic brain/spinal cord metastasis who are not planned for radiation, or who have been treated and are stable off steroids (or on a decreasing dose) and anticonvulsants are eligible. * Patients with significant cardiac disease, including: * any factors that increase the risk of QTc prolongation or risk of arrhythmic events (e.g. heart failure, hypokalaemia, congenital long QT syndrome, family history of long QT syndrome or unexplained sudden death under 40 years of age) or mean resting corrected QT interval (QTc) \> 470 msec * uncontrolled hypertension (BP ≥ 150/95 mmHg despite medical therapy) * acute coronary syndrome within 6 months prior to starting treatment * angina Canadian Cardiovascular Society Grade II-IV (despite medical therapy) * symptomatic heart failure (NYHA II-IV) * prior or current cardiomyopathy * atrial fibrillation with a ventricular rate \> 100 bpm at rest * severe valvular heart disease Patients with cardiac disease, who do not meet the exclusion criteria above, must have a baseline LVEF ≥ 50%. * Any evidence of severe or uncontrolled systemic disease, active infection, active bleeding diatheses or renal transplant, including any patient known to have hepatitis B, hepatitis C or human immunodeficiency virus (HIV). * Patients who have neuropathy \> grade 1 or other conditions precluding treatment with the standard chemotherapy regimen planned. Consult CCTG for patients with localised neuropathies as such patients may be eligible. * Patients who have significant gastrointestinal disease and who are unable to swallow capsules. * Patients on potent inhibitors or inducers of CYP3A4/5, CYP2C19 and CYP1A2 (must have discontinued within 2 weeks prior to randomization or 3 weeks for St. John's Wort). Patients who do not agree to avoid the ingestion of large amounts of grapefruit and Seville oranges (and other products containing these fruits, e.g. grapefruit juice or marmalade) and not take vitamin E supplements or multivitamin supplements. Patients who require oral anticoagulants (Coumadin) are eligible provided there is increased vigilance with respect to INR monitoring upon initiation of dosing with selumetinib. If medically appropriate and treatment available, the investigator should consider switching these patients to LMW heparin. * Patients with current or past history of central serous retinopathy or retinal vein occlusion, high intraocular pressure (≥ 21mm) or uncontrolled glaucoma (irrespective of IOP). Patients with visual symptoms should undergo ophthalmologic examination prior to randomization. * Pregnant or lactating women. Women of childbearing potential must have a urine pregnancy test proven negative within 7 days prior to randomization. Men and women of childbearing potential must agree to use adequate contraception * Patients who do not agree to avoid excessive sun exposure and use adequate sunscreen protection. * Selumetinib-specific precautions for patients of Asian ethnicity: Plasma exposure of selumetinib (Cmax and AUC) is higher, at a population level, in subjects of Asian descent by approximately 1.5- to 2-fold in non-Japanese Asians and Japanese subjects, compared with Western subjects. However, there is overlap in the range of exposure experienced by Asian and Western subjects and the higher average plasma exposure was not associated with a change in the tolerability profile of single dose selumetinib. Investigators should make a clinical judgment as to whether the potential risk of experiencing higher selumetinib plasma exposure and potential adverse events outweighs the potential benefit of treatment with selumetinib.